Convective/Storm Discussion Thread - 19th May 2018 onwards

[Supacell]

A new thread for all things convective around the UK going into the summer of 2018.

Old thread here:

Convective weather relating to Europe should go into here:

A chance of a few thunderstorms this week with central and southern parts of England and Wales looking most at risk. Although Monday is now moving into the reliable timeframe it is still too early to discuss specifics for the week as a whole. It is likely though that this week will provide some thundery showers or storms for a few of us. An easterly flow will probably favour more western areas for home grown storms, but elevated storms from the continent could also affect southern and south-eastern areas at times.

[Lauren]

Had the best storm in years last year, hoping to smash it this year.

[East_England_Stormchaser91]

To my mind, theres hints of a potential repeat of late May 1999 in some of the outputs, which kickstarted what was a fantastic year, arguably one of the best thundery summers the UK has seen. A trend which I hope is built upon this week. Some severe CAPE over the near continent is being shown at times, and steering winds look favourable for some potential imports from France and the Low Countries. 

[Summer Sun]

Day 1 Convective Outlook

VALID 06:00 UTC Sun 20 May 2018 - 05:59 UTC Mon 21 May 2018

ISSUED 15:56 UTC Sun 20 May 2018

ISSUED BY: Dan

A zone of slightly higher 850mb WBPT will drift westwards across SE England during the latter part of Sunday night and into Monday morning, along the northern edge of the main upper low situated over France. This may coincide with slight cooling aloft (particularly around 700mb) as a subtle shortwave drifts across the area, resulting in some elevated instability. Most model guidance remains dry, but there is a chance of a few high-based showers developing from elevated convection, with a low risk of some sporadic lightning. Confidence is rather low in this aspect.

http://www.convectiveweather.co.uk/forecast.php?date=2018-05-20

[Ben Sainsbury]

That time again for thunderstorm activity is upon us, let's take a look at how things are shaping up for tomorrow.

General consensus is for CAPE values to reach between 400-500J/kg in some of the more favourable locations tomorrow, severe parameters look relatively limited for tomorrow so no severe potential unfortunately. Saying that there is a possibility of seeing a FC or two tomorrow given decent LLS and wind convergence zones. 

Convergence zones along with strong heating look to be the prime factor for initiating storms and these are evident across much of East Wales/Central Areas along with parts of Dorset into Devon. Storms moving SW throughout the day and evening.

Beginning with the GFS: As always CAPE values are being well overcooked here by more than double. Storms I don't expect to be as widespread (and a little east compared to other models), though again Central Areas/CS-SW England are the most favourable locations.

 

Next the ECMWF: CAPE values not exceeding 400J/kg, similar to various Skew-T charts I've analysed. ECMWF has a main focus on Devon, although fewer showers across Central areas.

A last look at the NMM Model and EURO4: The NMM model showing the formation of several convergence zones across Central areas and the SW, although again the majority of the higher res models favoring much of the SW over Central areas.  

Therefore the general coverage of storms looks to be better over the SW regarding my forecast and if I had to choose a particular location tomorrow I'd have to say in and around the Yeovil area.

 

[Lauren]

Where are you seeing this? I can't see anything on the charts. Not being snarky, genuine question.

[Ben Sainsbury]

8 minutes ago, Lauren said:

Where are you seeing this? I can't see anything on the charts. Not being snarky, genuine question.

Can you elaborate, I'm not sure that I know what you mean?

[Lauren]

32 minutes ago, Ben Sainsbury said:

Can you elaborate, I'm not sure that I know what you mean?

Well I've looked at NetWeathers own graphs particularly CAPE and LI and it's not showing potential unless I'm looking at the wrong thing.

[Flash bang flash bang etc]

5 minutes ago, Lauren said:

Well I've looked at NetWeathers own graphs particularly CAPE and LI and it's not showing potential unless I'm looking at the wrong thing.

Several sources I’ve seen suggest this week to be potentially convectively active - though mainly confined to the south and usually in the afternoon / evening period.

Netweather itself mentioned it in their main forecast today.

[East_England_Stormchaser91]

16 minutes ago, Lauren said:

Well I've looked at NetWeathers own graphs particularly CAPE and LI and it's not showing potential unless I'm looking at the wrong thing.

Could well be some imports in your end of the woods Lauren. Much of this week showing some decent instability across the whole nearby continent with storms that will be travelling mainly Westwards-Northwestwards. Anything that fires up over Belgium, W Germany, Holland or NE France, keep an eye on it, it’s not very often we get to say that, as they are normally heading away from us at that point! 

[Flash bang flash bang etc]

Looking interesting for tonight with those storms over Holland at the moment and specks of high level cloud appearing overhead

[Flash bang flash bang etc]

Not expecting anything of note but some electrified showers later perhaps?

[Lauren]

17 minutes ago, East_England_Stormchaser91 said:

Could well be some imports in your end of the woods Lauren. Much of this week showing some decent instability across the whole nearby continent with storms that will be travelling mainly Westwards-Northwestwards. Anything that fires up over Belgium, W Germany, Holland or NE France, keep an eye on it, it’s not very often we get to say that, as they are normally heading away from us at that point! 

I'd love you to be correct!

[Supacell]

For the first half of the coming week any thunderstorms will be isolated as generally high pressure is in control of the weather. CAPE is looking quite decent, shear is not so and there are no weather fronts to provide additional triggers for thunderstorm development. So having read numerous forecasts and studied the charts I have come up with the following idea.

The forecast of warm sunshine for virtually everyone with just a few isolated heavy showers and thunderstorms breaking out would seem about right. Convergence zones will play a part tomorrow and I would not be surprised to see a number of showers and storms breaking out along narrow bands where convergence zones form. With very little wind shear any storms that form would likely pulse out quite quickly but this could then trigger further storms to develop along the outflow of the dying storm. Showers and storms will be moving slowly and in a direction slightly south of west. Initial developments will probably be somewhere to the west of London through the middle of the day and then expand westwards across Central Southern England. Further storms could also develop down the spine of the country and move into the West Midlands and NW England, although these are less likely than those further south. I agree with Ben's idea above and believe that somewhere around Wiltshire/Somerset may be best placed tomorrow for a late afternoon/evening storm.

Any storms that do form could have the potential to produce torrential downpours and gusty winds along with CG lightning. With slow storm motion there is the risk of localised flooding, especially considering the ground is currently quite dry and hard after what has been (and still is) a very dry spell of weather.

I am looking forward to the expert analysis on this one. If I was closer to the action I may have considered chasing, but currently the risk is not high enough for me to commit to such a long drive.

[East_England_Stormchaser91]

12 minutes ago, Lauren said:

I'd love you to be correct!

Talking of which, there’s one right now gone up north of Antwerp heading west!! 

[Summer Sun]

Day 2 Convective Outlook

VALID 06:00 UTC Mon 21 May 2018 - 05:59 UTC Tue 22 May 2018

ISSUED 19:26 UTC Sun 20 May 2018

ISSUED BY: Dan

 

... MONDAY MORNING ...

A shortwave will be sliding across SE England on Monday morning, rotating around the northern periphery of the main upper low over France. This will be accompanied by slight warming of the low-levels, while also cooling aloft. Some elevated convection seems likely during the morning hours over SE England, though the depth convection may be somewhat limited - hence uncertain if there will be much lightning activity.

 

... MONDAY AFTERNOON / EVENING ...

Nonetheless, this shortwave becomes the focus for deeper convection during the afternoon and evening hours as it continues to drift westwards. Model guidance varies in coverage and location of showers / thunderstorms, but 500-1,000 J/kg CAPE and low-level wind convergence/orographic forcing will likely aid the development of at least some isolated to widely-scattered showers and a few thunderstorms. A marked dewpoint boundary over the northern / western Home Counties might also aid initiation. A SLGT has been issued where better multi-model consensus exists, though isolated thunderstorms may be possible farther north over NW England, for example.

 

Deep layer shear is rather weak, and so convection will be poorly-organised and pulse-type (an individual thunderstorm will only have a life cycle of less than 1 hour for example). Main threat will be localised surface water flooding (due to slow motion of showers) and gusty winds (particularly when showers/storms collapse at the end of their life cycle). Hail up to 1.0cm in diameter will be possible with the strongest cells. Main uncertainty involves just how many showers may actually develop, and then whether they become deep enough to produce much in the way of lightning given the weakly-sheared environment. Some uncertainty also exists over the exact W-E position of the SLGT area in E Wales / W Midlands, which may need to be adjusted.

 

Any showers / thunderstorms that do develop will begin to fade towards sunset as nocturnal cooling of the boundary layer commences.

 

... MONDAY NIGHT ...

Upper low over NE France will drift close to SE England on Monday night. On its northern flank, higher 850mb WBPT airmass will attempt to advect across the North Sea from the nearby Continent, though some uncertainty as to how far west this will reach, depending on the shape/location of the upper low.

 

Elements of medium-level instability are likely to spread west from NE France / BeNeLux towards East Anglia and SE England, and so it is possible some elevated showers or thunderstorms may drift in this general direction during Monday night, but probably with a weakening trend as instability reduces as one comes further west. For now, have refrained from issuing a SLGT, but one may be required if conditions improve.

 

http://www.convectiveweather.co.uk/forecast.php?date=2018-05-21

[Azazel]

I’ve seen a few posters say this is similar to the setup we had in late May 1999.

 

i remember going to Florida on the first of June I’m pretty sure, so would’ve been last day of May. I was 14.

We had a storm pass through Whitchurch, Hants which is still to this day the most violent little storm I’ve ever seen. Full daytime darkness which I’ve not seen before or since, the sky went sea green and the rotation was incredible - genuinely looked like CGI, it was crazy.

 

if any posters can confirm the date and setup for me that would be fab. 

[Supacell]

1 hour ago, Azazel said:

I’ve seen a few posters say this is similar to the setup we had in late May 1999.

 

i remember going to Florida on the first of June I’m pretty sure, so would’ve been last day of May. I was 14.

We had a storm pass through Whitchurch, Hants which is still to this day the most violent little storm I’ve ever seen. Full daytime darkness which I’ve not seen before or since, the sky went sea green and the rotation was incredible - genuinely looked like CGI, it was crazy.

 

if any posters can confirm the date and setup for me that would be fab. 

If it was at the end of May then I believe you will be thinking about severe storms that occurred on the 29th May 1999:

I have also heard people comparing the set up to the 9/10th May 2001:

 

[Nick F]

Been a while since I've written in this thread, or indeed anywhere on the forum, such has the weather had little of note worth talking about. But as it looks like there is a risk of storms, albeit isolated, most days in the south and west this week, I'm back and with a Netweather Thunderstorm Outlook for Monday.

Storm & Convective Forecast

Issued 2018-05-20 21:46:39
Valid: 21/05/2018 0600Z - 22/05/2018 0600Z

THUNDERSTORM OUTLOOK - DAY 1 (MONDAY 21ST MAY 2018)

Synopsis

A broad upper trough covers the far N Atlantic with an upper ridge centred over Scandinavia/Baltic Sea. A weak upper low with cooler air aloft over near continent will drift westward across England and Wales in next 24 hours which, combined with diurnal heating of increasingly moist surface flow, will be the catalyst for isolated thunderstorms to develop across southern and western areas on Monday.

… S, CENTRAL AND W ENGLAND + WALES …

Weak and diffuse upper low/trough  drifting west across Sern Britain will introduce subtle cooling aloft in the mid-levels atop moistening weak low-mid level flow from the east overnight and through Monday … this will steepen lapse rates … initially bringing some weak mid-level instability to E/SE England early Monday, which may produce spotty showers. Diurnal surface heating will then increase surface instability into the afternoon, as sunshine warms a moistening airmass (dew points in low-mid teens C) beneath mid-levels cooling from the east, resulting in around 500-1000 j/kg CAPE. This environment should promote the development of isolated thunderstorms across S England, perhaps a little more numerous across W England and E Wales – where weak surface convergence is indicated.

Weak vertical shear will limit potential of severe weather from any storm to a low risk, though hail is possible given predicted CAPE and an isolated incidence of large can’t be ruled out … localised flooding may be a greater risk given slow-moving nature of any storms. Storms will generally die out after dark as heating wanes, though there is a risk of elevated instability/convection returning to the SE Monday night, which may bring isolated lightning.

Forecast here as well: https://www.netweather.tv/weather-forecasts/uk/convective

Edited May 20, 2018 by Nick F

[Windblade]

I mean no offence to any forecasters when I say this but due to the way things always seem to pan out I'm taking any and all storm forecasts with a gigantic bucket of salt until I actually see a storm. Everytime I look to be in with a decent chance something always goes wrong so I'm playing the pessimistic card in the hope I am wrong.

[Lauren]

45 minutes ago, Windblade said:

I mean no offence to any forecasters when I say this but due to the way things always seem to pan out I'm taking any and all storm forecasts with a gigantic bucket of salt until I actually see a storm. Everytime I look to be in with a decent chance something always goes wrong so I'm playing the pessimistic card in the hope I am wrong.

This is my tactic too. Been burnt far too many times. Until I see a storm, there will be no excitement  (well, a little).

[Windblade]

Yep. Last time out things looked almost certain for me to see one of the best, most active storms in years. It came all the way from northwest france, got within spitting distance and then just died, literally as if someone had flicked the off switch. Not so much as a rumble. I'm still reeling from that one. 

Edited May 21, 2018 by Windblade

[dave reid]

Morning all. 

That time of year again where we all get ridiculously excited and generally massively disappointed. 

I'll be finishing work climbing Telecom towers (hopefully before any storms fire) and heading out on the road today for my first chase of the year.

Wish me luck luck and I'll post any cool pics or vid should the thunder god's smile on me 

[Michellelovescats]

was that the one a month ago sat night 21st april? that one started at 7pm here (south coast near iow) and went on til nearly 2am came from france (we had some short spells without storms but most of that time there was at least distant lightning)

[Guest]

Given summer doesn't start until next Friday with the forecast looking juicy to say the least over the next 7 or 8days lts quite possible spring 2018 will have delivered more electrical excitement down here in the south than many of the summers from 2003-2016. Last months lightshow was probably in the top 5 of living in Bournemouth for 24 years now.